1. Field of the Invention
The present invention relates to a methanol oxidation catalyst and a method for producing the methanol oxidation catalyst.
2. Description of the Related Art
Solid polymer type fuel cells, and particularly solid polymer type fuel cells using an aqueous methanol solution as fuel converts chemical energy into electric power by the catalytic reaction of an electrode. Therefore, a highly active catalyst is essential to develop a high-performance fuel cell.
The theoretical voltage obtained by the catalytic reaction of the electrode is 1.21V, whereas the voltage loss due to the PtRu catalyst is about 0.3V. Therefore, an anode catalyst having high activity (methanol oxidation activity) over PtRu is desired. In the meantime, current PtRu anode catalysts have problems due to elution of Ru, and therefore, highly active methanol oxidation catalysts having a low Ru content and Ru-free composition are desired.
Studies have been made as to methanol oxidation catalysts having various composition types so far. For example, a method in which metals such as tungsten, tantalum and niobium are added is described in U.S. Pat. No. 3,506,494. In Jpn. Pat. Appln. KOKAI Publication Nos. 2004-281177 and 2006-179445, there are descriptions concerning a sputtering process. There are only a few reports as to a reduction in the amount of Ru to be added and Ru-free compositions.
Because the catalysts are nanoparticles, the surface electron state of the catalyst particles and the nano-structure of the particles are strongly dependent on the type and amount of elements to be added. In order to obtain high activity and high stability, it is necessary that the type and amount of the elements to be added and a combination of elements are made to be appropriate. Studies concerning catalyst compositions and processes are insufficiently made and a highly stable catalyst having sufficient methanol oxidation activity has not been established yet.